1. Field of the Invention
The present invention relates to a photosensitive resistant resin precursor composition having an excellent film thickness uniformity and which is suitably used for a surface protection layer and an insulating interlayer of a semiconductor element, an insulating layer of an organic electroluminescent device, and the like.
2. Description of the Related Art
For the surface protection layer and insulating interlayer of semiconductor elements, a heat resistant polyimide resin having excellent electric characteristics and mechanical characteristics has been used. On the other hand, a technique of giving photosensitivity to a polyimide resin precursor composition has been of interest from the viewpoint of simplification of a patterning operation, reduction of process steps, and increase of yields. Also, a positive photosensitive resin precursor composition capable of being developed with an alkaline solution has recently been developed form the viewpoint of safety, ease of handling, and environmental concerns.
In general, to form a film, these photosensitive resin precursor compositions are applied onto a substrate, such as a silicon wafer or glass, by spin coating and heated to evaporate the solvent. Good solvents, such as N-methyl-2-pyrrolidone and γ-butyrolactone, are generally used as the solvent in this operation. However, since these solvents have a boiling point as high as 200° C. or more, they are difficult to vaporize during spin coating, and they must be heated to vaporize rapidly. Consequently, it is difficult to form a film having a uniform thickness. The use of a solvent easy to vaporize disadvantageously results in precipitation of foreign matter because the solvent cannot dissolve the resin well, or causes striation during spin coating even if the solvent dissolve the resin.
A use of diacetone alcohol for a cresol novolac resin has been disclosed in Japanese Unexamined Patent Application Publication No. 7-128848. However, since heat resistant resin precursors epitomized by a polyimide resin precursor have low solubilities in solvents by nature, they cannot be satisfactorily dissolved even in diacetone alcohol.